Color converting device emphasizing a contrast of output color data corresponding to a black character

ABSTRACT

A color converting device converts input CMYK data into output color data in a predetermined different format. The color converting device comprises a contrast emphasizing unit emphasizing a contrast of the output color data corresponding to the CMYK data representing a black-character color more than a contrast of the output color data corresponding to the CMYK data representing a non-black-character color.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a color conversion technologyof CMYK data, and more particularly, to a color converting device, acolor converting method, and a recording medium storing color printersoftware operated in a workstation, for converting CMYK print data (acolor image signal) generated in an image forming device, such as acolor copying machine, a color printer, or a color facsimile, into colordata (a color signal) in a different format suitable for displaying on acolor display or printing from another color printer.

2. Description of the Related Art

There are a lot of conventional technologies regarding a colorconversion of CMYK data.

For example, a memory map interpolative calculation method using afour-dimensional lookup table is one of general color converting methodsfor converting color data (CMYK image data) consisting of four colorcomponents such as CMYK into RGB image data. (e.g., Japanese Patent No.2,903,808 and Japanese Laid-Open Patent Application No. 57-208765)

The above-mentioned memory map interpolative calculation method realizesa highly precise color conversion throughout a color space. The methodcomprises the steps of dividing a four-dimensional color space formed byfour color signals into a plurality of five-vertex solids, selecting afive-vertex solid including an input color by using higher-order bits ofinput data (an input signal), and reading an interpolative calculationintensity corresponding to the selected five-vertex solid from afour-dimensional lookup table so as to perform a linear interpolativecalculation.

Other means for converting CMYK image data into RGB image data include adevice described in Japanese Laid-Open Patent Application No. 9-284579.This device performs a four-dimensional interpolative calculation bylinearly interpolating results of a plurality of three-dimensionalinterpolative calculations. For example, the four-dimensionalinterpolative calculation can be performed to input CMYK signals byperforming a plurality of three-dimensional interpolative calculationsof a C-M-Y space, selecting two of results of the three-dimensionalinterpolative calculations according to higher-order bits of a K signal,and linearly interpolating the selected two results by lower-order bitsof the K signal.

However, the above-mentioned memory map interpolative calculationmethod, which divides a cubic unit into 24 five-vertex solids, requiresjudging processes in 24 patterns using lower-order bits of the inputsignal. Although these judging processes can be processed in parallelwhen performed by means of hardware, these judging processes claim along time to successively compare the lower-order bits with each otherto find a larger bit in each (magnitude relation) comparison whenperformed by means of software (in a CPU).

As to the above-mentioned device described in Japanese Laid-Open PatentApplication No. 9-284579, since the device performs a plurality of thethree-dimensional interpolative calculations in parallel, thethree-dimensional interpolative calculations claim quite a long timewhen processed by a CPU. For instance, performing a four-dimensionalinterpolative calculation in which each of axes C, M, Y and K is dividedinto 8 entails a total of nine three-dimensional interpolativecalculations corresponding to K signals in nine patterns.

Also, there is a method for printing CMYK print data by another colorprinter. This method comprises the steps of converting CMYK data into adevice-independent Lab signal, correcting the Lab signal so as tofaithfully reproduce a ground color, performing a contrast control forenhancing a visibility of a highlight when not reproducing the groundcolor, and thereafter converting the Lab signal into CMYK data used foranother color printer. (Japanese Laid-Open Patent Application No.8-212324)

It is well known that a hardcopy image printed on such a printer as acolor printer and a softcopy image displayed on such a display as a CRTdisplay are perceived as differently looking colors because of utterlydifferent color reproducing methods applied to the images, though theimages are based on same image data. Thereupon, there is a method formaking the hardcopy image and the softcopy image perceived asidentically looking colors. This method comprises the steps ofequalizing a dynamic range of input color data and a dynamic range ofoutput color data, creating a color conversion profile by using achromatic adaptation model so that the hardcopy image and the softcopyimage become perceptually identical, and performing a color conversionby using the color conversion profile. (Japanese Laid-Open PatentApplication No. 11-112819)

Some of image forming devices such as color printers and color copyingmachines can generate CMYK data in the devices themselves and store theCMYK data in an inner storage device such as a hard disk so as to usethe CMYK data repeatedly. This stored CMYK data can be converted intoRGB data more reusable in a computer so as to be displayed as a softcopyimage on a display connected to the computer. Furthermore, this RGB datadisplayed on the display can be processed as by adding characters orsymbols thereto, and this processed digital image data can be reproducedagain as a hardcopy.

However, simply converting the stored CMYK data into the RGB data andtransmitting the RGB data to the computer so as to display the RGB dataon the display or print the RGB data on another color printer may notpossibly result in a high-quality image. Especially the reproductionquality of a black character is noticeably deteriorated.

This is because the CMYK data generated in the image forming device hasa characteristic optimized for a hardcopy. For example, when a colorcopying machine prints a black character by overlapping four colors ofCMYK, displacement of each color reduces the sharpness and legibility ofthe black character. Thereupon, the color copying machine often performsan image area separation process which extracts edge parts of a blackcharacter so as to print the edge parts monochromatically with the colorof K, and separates the color of other pictorial parts into the fourcolors of CMYK so as to use inks of all the four colors. Likewise, acolor printer performs an object-suited chromatic process which judges adraw code in a printer driver so as to print a black charactermonochromatically with the color of K, and separate the color of otherparts into the four colors. However, simply converting such CMYK dataincluding a black character part and other parts undergoing differentcolor reproduction methods into RGB data, etc. cannot gain ahigh-quality black character reproduction in displaying on a display orprinting from another color printer.

Additionally, the above-mentioned technology disclosed in JapaneseLaid-Open Patent Application No. 8-212324 basically enables a faithfulcolor reproduction by converting CMYK data into colorimetrically equalCMYK data, because the technology is aimed at a conversion betweenhardcopy output signals. However, in a case where the CMYK data isconverted into RGB data used for displaying and then is output to acolor printer via a printer driver, the printer driver often performs acolor correction equalizing a dynamic range of a monitor to a dynamicrange of a color printer output. Accordingly, simply equalizingreference whites of CMYK data and RGB data results in an insufficientdensity of black in the printer output.

On the other hand, since the above-mentioned technology disclosed inJapanese Laid-Open Patent Application No. 11-112819 equalizes a dynamicrange of input color data and a dynamic range of output color data, thistechnology can convert the input color data into the output color datasuitable for a screen display, and also can prevent the above-mentioneddecrease in black density when outputting the color data to anothercolor printer via a printer driver. However, since this conventionaltechnology is aimed at input color data read from a hard copy by ascanner or input by a digital camera, the technology cannot be appliedto CMYK data subjected to the above-described image area separationprocess or the above-mentioned object-suited chromatic process becauseof problems such as that the technology cannot determine a black point(a darkest point) of the CMYK data.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a colorconverting device and method, and a color conversion profile creatingdevice and method, in which the above-mentioned problems are eliminated.

A more specific object of the present invention is to provide a colorconverting device converting CMYK print data generated in an imageforming device, such as a color printer, a color copying machine, or acolor facsimile, into RGB data or the like which enables a high-qualityblack character reproduction in displaying on a display or printing fromanother color printer, to provide a method and a device of creating acolor conversion profile used in the color converting device, and toprovide a color converting device and method capable of performing athigh speed an interpolative calculation for n-dimensional data (n>=4)preferable in a software processing.

In order to achieve the above-mentioned objects, there is providedaccording to one aspect of the present invention a color convertingdevice converting input CMYK data into output color data in apredetermined different format, the device comprising:

a contrast emphasizing unit emphasizing a contrast of the output colordata corresponding to the CMYK data representing a black-character colormore than a contrast of the output color data corresponding to the CMYKdata representing a non-black-character color.

According to one of two types of the above-mentioned contrastemphasizing unit, there is provided according to another aspect of thepresent invention a color converting device converting input CMYK datainto output color data in a predetermined different format, the devicecomprising:

a color conversion profile representing a correspondence of the CMYKdata with the output color data; and

a color converting unit converting the CMYK data into the output colordata by referring to the color conversion profile,

wherein the color conversion profile has a characteristic of emphasizinga contrast of the output color data corresponding to the CMYK datarepresenting a black-character color more than a contrast of the outputcolor data corresponding to the CMYK data representing anon-black-character color.

According to the other of the two types of the above-mentioned contrastemphasizing unit, there is provided according to another aspect of thepresent invention a color converting device converting input CMYK datainto output color data in a predetermined different format, the devicecomprising:

a CMYK/colorimetric-value conversion unit converting the CMYK data intoa calorimetric value to be measured with respect to an image formed fromthe CMYK data by an image forming device;

a black-character color judging unit judging whether or not the CMYKdata represents a black-character color;

a calorimetric value correction unit correcting the calorimetric valueby performing a contrast correction appropriate for a black-charactercolor to the calorimetric value converted by the CMYK/colorimetric-valueconversion unit from the CMYK data judged to represent theblack-character color by the black-character color judging unit, and byperforming a contrast correction appropriate for a non-black-charactercolor to the colorimetric value converted by the CMYK/colorimetric-valueconversion unit from the CMYK data judged to represent thenon-black-character color by the black-character color judging unit; and

a colorimetric-value/output-color-data conversion unit converting thecalorimetric value corrected by the calorimetric value correction unitinto the output color data,

wherein a contrast of the output color data corresponding to the CMYKdata judged to represent the black-character color is emphasized morethan a contrast of the output color data corresponding to the CMYK datajudged to represent the non-black-character color.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention a color conversionprofile creating device creating a color conversion profile used forconverting CMYK data into output color data in a predetermined differentformat, the device comprising:

a CMYK data generation unit generating the CMYK data;

a calorimetric value converting unit converting the CMYK data generatedby the CMYK data generation unit into a calorimetric value to bemeasured with respect to an image formed from the CMYK data by an imageforming device;

a black-character color judging unit judging whether or not the CMYKdata generated by the CMYK data generation unit represents ablack-character color;

a calorimetric value correcting unit correcting the calorimetric valueby performing a contrast correction appropriate for a black-charactercolor to the calorimetric value converted by the calorimetric valueconverting unit from the CMYK data judged to represent theblack-character color by the black-character color judging unit, and byperforming a contrast correction appropriate for a non-black-charactercolor to the colorimetric value converted by the colorimetric valueconverting unit from the CMYK data judged to represent thenon-black-character color by the black-character color judging unit; and

a color conversion profile setting unit setting the color conversionprofile by using the colorimetric value corrected by the colorimetricvalue correcting unit,

wherein the color conversion profile has a characteristic of emphasizinga contrast of the output color data corresponding to the CMYK datarepresenting the black-character color more than a contrast of theoutput color data corresponding to the CMYK data representing thenon-black-character color.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention a color conversionprofile creating method creating a color conversion profile used forconverting CMYK data into output color data in a predetermined differentformat, the method comprising:

the CMYK data generating step of generating the CMYK data;

the calorimetric value converting step of converting the CMYK datagenerated by the CMYK data generating step into a colorimetric value tobe measured with respect to an image formed from the CMYK data by animage forming device;

the black-character color judging step of judging whether or not theCMYK data generated by the CMYK data generating step represents ablack-character color;

the calorimetric value correcting step of correcting the calorimetricvalue by performing a contrast correction appropriate for ablack-character color to the calorimetric value converted by thecalorimetric value converting step from the CMYK data judged torepresent the black-character color by the black-character color judgingstep, and by performing a contrast correction appropriate for anon-black-character color to the calorimetric value converted by thecalorimetric value converting step from the CMYK data judged torepresent the non-black-character color by the black-character colorjudging step; and

the color conversion profile setting step of setting the colorconversion profile by using the calorimetric value corrected by thecalorimetric value correcting step,

wherein the color conversion profile has a characteristic of emphasizinga contrast of the output color data corresponding to the CMYK datarepresenting the black-character color more than a contrast of theoutput color data corresponding to the CMYK data representing thenon-black-character color.

According to the present invention, CMYK data of an image formingdevice, such as a color printer or a color copying machine, containingblack-character parts and non-black-character parts undergoing differentcolor reproduction methods can be appropriately converted into colordata in a different format, which enables a high-quality black characterreproduction in displaying on a display or printing from another colorprinter.

In order to achieve the above-mentioned objects, there is also providedaccording to another aspect of the present invention a color convertingdevice converting an input color signal into an output color signal(RGB) by dividing an 4-dimensional input color space (CMYK) into aplurality of 16-vertex units to be selected according to higher-orderdata of the input color signal, dividing one of the 16-vertex units intoa plurality of six 8-vertex solids (T1 to T6) to be selected accordingto lower-order data of the input color signal, and performing aninterpolative calculation using interpolation coefficients (P0 to P15)corresponding to one of the 8-vertex solids to which the input colorsignal belongs, the device comprising:

storing means for storing 4-dimensional interpolation coefficients (P0to P15) corresponding to each of the 8-vertex solids (T1 to T6);

determining means for determining which one of the 8-vertex solids theinput color signal belongs to according to a magnitude relation amongthe lower-order data;

reading means for reading the 4-dimensional interpolation coefficientscorresponding to the determined one of the 8-vertex solids from thestoring means;

generating means for generating 3-dimensional interpolation coefficients(Pa to Pd) used for a 3-dimensional interpolative calculation from the4-dimensional interpolation coefficients; and

interpolating means for performing the 3-dimensional interpolativecalculation by using the lower-order data and the 3-dimensionalinterpolation coefficients.

According to the present invention, the color converting device enablesa color conversion of an input signal having four dimensions or more tobe performed at high speed even by means of a CPU, and also enables theselection from among the polyhedral units to be performed at high speed.

According to the present invention, the color converting device alsoenables a color conversion of such a color signal as multiband datacontaining a multitude of color components to be performed at highspeed.

According to the present invention, the color converting device alsoenables a sum-of-products calculation suitable for a CPU processing tobe performed at high speed.

According to the present invention, the color converting device alsoenables a color conversion of an multi-dimensional input signal to beperformed at high speed even by means of a CPU incapable of acceleratinga sum-of-products calculation.

According to the present invention, the color converting device shortensan access time of a lookup table upon performing a color conversion ofan input signal having four dimensions or more.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of an image processingsystem according to the present invention;

FIG. 2 is a block diagram used for explaining a process of generatingprint data of a color printer, and a printer controlling device;

FIG. 3 is a block diagram of a first embodiment of a color convertingdevice according to the present invention;

FIG. 4 is a block diagram of an embodiment of a color conversion profilecreating device according to the present invention;

FIG. 5 is a flow chart of an embodiment of a color conversion profilecreating procedure according to the present invention;

FIG. 6 is a graph used for explaining an example of a contrastconversion table;

FIG. 7 is a block diagram of a second embodiment of the color convertingdevice according to the present invention;

FIG. 8A is an illustration comparing binary CMYK data in ablack-character part with multivalued data thereof;

FIG. 8B is an illustration comparing binary CMYK data in a pictorialpart with multivalued data thereof;

FIG. 9 is a graph used for explaining another example of a contrastconversion table;

FIG. 10 is a block diagram of a third embodiment of the color convertingdevice according to the present invention;

FIG. 11 is a block diagram of a configuration of a color copyingmachine;

FIG. 12 is an illustration of a large-size character image printed by acolor copying machine;

FIG. 13 is a block diagram of a fourth embodiment of the colorconverting device according to the present invention;

FIG. 14 is a schematic diagram of another embodiment of an imageprocessing system according to the present invention;

FIG. 15 illustrates a 16-vertex unit;

FIG. 16 illustrates six 8-vertex solids;

FIG. 17 shows expressions used in selecting an 8-vertex solid;

FIG. 18 is an illustration used to explain an interpolative calculationmethod according to the present invention;

FIG. 19 shows correspondences between the 8-vertex solids andcoefficients α, β, γ and δ;

FIG. 20 is a block diagram of an example of a computer performing acolor converting operation;

FIG. 21 is a flowchart of an interpolative calculation process;

FIG. 22 is a flowchart of an 8-vertex solid judging (determining)process;

FIG. 23 illustrates two 12-vertex solids;

FIG. 24 is a block diagram of an example of the present inventionrealized by means of hardware;

FIG. 25 is a flowchart of a color converting operation according toanother embodiment of the present invention; and

FIG. 26 exemplifies a hardware configuration of an image processingsystem in which the present invention is realized by means of softwarerecorded on a recording medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given, with reference to the drawings, ofembodiments according to the present invention.

[Embodiment of an Image Processing System]

FIG. 1 is a schematic diagram of an embodiment of an image processingsystem according to the present invention. In FIG. 1, an image formingdevice 100 forms an image by using CMYK data for outputting a hard copythereof. Specifically, the image forming device 100 is a color printer,a color copying machine, a color facsimile device, etc. The imageforming device 100 can output the above-mentioned CMYK data to a colorconverting device 104 of the present invention. The color convertingdevice 104 has a color-converting function of converting the CMYK datainto RGB data. A computer 102 is a personal computer, etc. Softwareincluding various applications and printer drivers can be installed intothe computer 102. The computer 102 can display the RGB data transmittedfrom the color converting device 104 on a display 103. The computer 102can also output the RGB data to a color printer 101 by activating aprinter driver corresponding to the color printer 101. The color printer101 receives the drawing data of the RGB format from the computer 102,and outputs a hard copy thereof. This color printer 101 incorporates aprinter controlling device 105 converting the drawing data of the RGBformat received from the computer 102 into CMYK data used for printing.

Besides, the printer controlling device 105 can be provided as a deviceindependent from the color printer 101. Further, part of functions ofthe printer controlling device 105 can be taken over by the printerdriver of the computer 102, etc.

Similarly, although the color converting device 104 of the presentinvention can be provided as an independent device, the function of thecolor converting device 104 may be executed by means of software in thecomputer 102, for example. Further, the color converting device 104 canbe mounted in the image forming device 100. The scope of the presentinvention embraces the image forming device 100 thus incorporating thecolor converting device 104.

Next, a description will be given of operations of the above-mentionedimage processing system as a whole. The image forming device 100 storesthe CMYK data generated in the process of outputting a hard copy, in abuilt-in hard disk. An operation of outputting a hard copy means aprinting operation using a color printer or a copying operation using acolor copying machine, for example. The CMYK data generated in the imageforming device 100 is transferred to the color converting device 104upon the generation thereof or when ordered to be transferred. The colorconverting device 104 converts the CMYK data into the RGB data byperforming a color conversion to the CMYK data, and transmits the RGBdata to the computer 102 immediately or when ordered to transmit the RGBdata. The computer 102 retains the RGB data in a storage medium such asa hard disk provided therein. An operator of the computer 102 can viewan image of the RGB data by displaying the RGB data stored in thecomputer 102 on the display 103 as occasion arises, can process the RGBdata by using suitable applications, and can supply the original RGBdata or the processed RGB data to the color printer 101 so as to havethe RGB data printed.

[Description of the Image Forming Device 100: as a Color Printer]

Next, a description will be given, with reference to FIG. 2, ofoperations of generating the CMYK data, and structures related thereto,when the image forming device 100 is a color printer.

In FIG. 2, a computer 200 transmits a draw command to the image formingdevice 100, and is connected to the image forming device 100 via aninterface cable or a network. It is noted that the computer 102 shown inFIG. 1 can function as this computer 200. A printer controlling device210 of the image forming device 100 may have a similar configuration tothat of the printer controlling device 105 of the color printer 101shown in FIG. 1, and comprises a color converting unit 211, a renderingunit 212, a band buffer 213, a gradating unit 214, and a storage device215, for example. This printer controlling device 210 may be mounted inthe image forming device 100, or may be an independent device. Further,part of functions of the printer controlling device 210 can be takenover by a printer driver of the computer 200, etc.

An operator of the computer 200 can edit or create document data 204 byusing such means as an application 201 installed in the computer 200.After completing the document data 204, the operator orders a printingso as to print the document data 204 by using the image forming device100. When the computer 200 receives a printing command via theapplication 201, the computer 200 transmits the document data edited orcreated in the application 201 to a printer driver 202. The printerdriver 202 converts the document data into a draw command of an RGBformat so as to make the document data receivable by the printercontrolling device 210, temporarily stores the draw command of the RGBformat in a recording medium 203, such as a hard disk, if necessary, andtransmits the draw command of the RGB format to the printer controllingdevice 210 in synchronization with printing operations of the colorprinter (the image forming device 100).

When the printer controlling device 210 receives the draw command, theprinter controlling device 210 converts the draw command of the RGBformat into a draw command of a CMYK format in the color converting unit211. In this process, the color converting unit 211 performs a colorconversion process appropriate for attributes of draw objects whileinterpreting the draw command, and transmits the obtained draw commandof the CMYK format to the rendering unit 212. The rendering unit 212converts the data of the command format into CMYK data of a rasterformat, and stores the CMYK data in the band buffer 213. The CMYK dataof the raster format is read from the band buffer 213, and is subjectedto a gradation conversion in the gradating unit 214. The gradating unit214 applies such a process as a dither to the CMYK data so as to convertthe CMYK data into print data having a number of gradations processibleby an image-forming engine of the image forming device 100, andtemporarily stores the print data in the storage device 215, such as ahard disk. For example, in a case where the image-forming engine of theimage forming device 100 forms a hard copy by using inks of C (cyan), M(magenta), Y (yellow) and K (black) where each of the colors can beshaded in 256 gradations, the CMYK data of the raster formatrepresenting each of the colors in 8 bits is stored in the storagedevice 215 as the print data. In another case where the CMYK data isbinarized by a dither process, the CMYK data of the raster formatrepresenting each of the colors in one bit is stored in the storagedevice 215. Thereafter, the CMYK data is read from the storage device215 in timing with a printing speed of the image forming device 100, andis printed out as a hard copy by the image-forming engine.

Hereinbelow, a specific description will be of the (object-suited) colorconversion process appropriate for various attributes of draw objectsperformed in the color converting unit 211. Obtaining a high-definitionhard copy generally requires different color reproduction methods to beused in accordance with different attributes of objects. Especially,different color reproduction methods are generally used to reproduce thecolor of a black character and to reproduce the color of a gradationalimage such as a photographic image, even though both are black (R=G=B=0)as RGB data. In other words, reproducing a black character by using thefour colors of CMYK causes a problem of displacement of dots of eachcolor upon outputting a hard copy resulting in a blurred character whichis hard to read. In addition, when reproducing a black character byoverlapping the four colors, it is difficult to maintain a balance amongthe four colors, causing a problem of unwanted appearances of the colorsin the black character. On the other hand, reproducing a black color ina shadow area of a photographic image only by using an ink of K (black)causes a problem of discontinuous gradations because it is hard tomaintain a continuity of the black-colored part with otherchromatic-colored parts. Therefore, different color reproduction methodsare generally used in which a black character is reproduced solely bythe color of K (black) while a black part in a photographic imagecharacter is reproduced by using the four colors of CMYK.

However, a high-quality black character reproduction cannot be achievedin displaying on the display 103 or reprinting from the other colorprinter 101 simply by converting the CMYK data optimized for a hard-copyoutput by the above-mentioned object-suited color conversion processinto, for example, RGB data without any contrivances, and supplying theRGB data to the computer 102. Thereupon, the color converting device 104of the present invention performs a color conversion converting the CMYKdata optimized by the above-mentioned object-suited color conversionprocess (or CMYK data subjected to an image area separation process in acolor copying machine described hereinafter in detail) into, forexample, RGB data which enables a high-quality black characterreproduction in displaying on the display 103 or reprinting from theother color printer 101.

[First Embodiment of the Color Converting Device 104]

FIG. 3 is a block diagram of a first embodiment of the color convertingdevice 104 according to the present invention. In FIG. 3, the colorconverting device 104 comprises a color converting unit 120 and a colorconversion profile storage unit 121. The color converting unit 120 andthe color conversion profile storage unit 121 together form a contrastemphasizing unit. The color conversion profile storage unit 121 stores acolor conversion profile representing correspondences of CMYK data asinput data with RGB data as output color data. The color converting unit120 refers to the color conversion profile so as to convert input CMYKdata into output RGB data.

According to the present invention, the color conversion profile storageunit 121 stores the color conversion profile having a characteristic ofemphasizing a contrast of RGB data (output color data) corresponding toCMYK data representing a black-character color (the color of a blackcharacter) more than a contrast of RGB data corresponding to CMYK datarepresenting a non-black-character color. Accordingly, the CMYK datarepresenting the black-character color is converted into the RGB datawith the emphasized contrast. Therefore, a high-quality black characterreproduction can be achieved in displaying on the display 103 orprinting on the color printer 101 by the color converting device 104 ofthe present invention converting the CMYK data subjected to theabove-mentioned object-suited color conversion process (as CMYK data forprinting in a color printer) into the above-mentioned RGB data, andsupplying the RGB data to the computer 102. Besides, colors other thanthe black-character color are reproduced faithfully with subduedcontrasts.

The color converting device 104 of the present invention adopts a memorymap interpolative calculation method using a widely knownfour-dimensional lookup table (4D-LUT). Accordingly, the colorconversion profile storage unit 121 stores the color conversion profileas a four-dimensional lookup table. The color converting unit 120comprises a grid-point address generation unit 123 and an interpolativecalculation unit 124. The grid-point address generation unit 123generates addresses of vertices of an interpolation solid to which aninput color represented by input CMYK data belong (representative pointsin a four-dimensional color space defined by four CMYK components;hereinafter referred to as grid points) by using higher-order bits andlower-order bits of the input CMYK data (e.g., 8 bits for each of thecolors), and supplies the addresses to the color conversion profilestorage unit 121. The interpolative calculation unit 124 performs aninterpolative calculation by using grid-point output values(interpolation parameters) read from the color conversion profilestorage unit 121 and using lower n bits of the CMYK data so as tocalculate a value of RGB data corresponding to the CMYK data.

Besides, publicly known documents related to the memory mapinterpolative calculation method adopted in the present embodimentinclude publications of Japanese Laid-Open Patent Application No.57-208765 and Japanese Patent No. 2,903,808. These publications disclosea five-point interpolation method for realizing a highly precise colorconversion throughout a color space. The five-point interpolation methodcomprises the steps of dividing a four-dimensional color space definedby four color components into a plurality of five-vertex solids,selecting a five-vertex solid including an input color by usinghigher-order bits of input data, and reading an interpolativecalculation intensity corresponding to the selected five-vertex solidfrom a four-dimensional lookup table so as to perform a linearinterpolative calculation. The color converting unit 120 of the presentembodiment may perform a similar interpolative calculation method. Thatis, since the feature of the present embodiment lies in thecharacteristic of the color conversion profile used in the interpolativecalculation, no further description will be given of the interpolativecalculation.

[Embodiments of a Device and a Method of Creating the Color ConversionProfile]

Next, a description will be given of a device and a method of creatingthe color conversion profile (the four-dimensional lookup table) havingthe above-described characteristic which is to be stored in the colorconversion profile storage unit 121 shown in FIG. 3.

FIG. 4 is a block diagram of an embodiment of a color conversion profilecreating device according to the present invention. FIG. 5 is a flowchart of an embodiment of a color conversion profile creating procedureaccording to a color conversion profile creating method of the presentinvention. The color conversion profile creating device shown in FIG. 4performs step S102 and the following steps shown in FIG. 5.

It is noted that the color conversion profile creating device may bemounted to the color converting device 104 or the image forming device100, or may be provided as an independent device. The present inventionencompasses the color converting device 104 or the image forming device100 thus incorporating the color conversion profile creating device.

In FIG. 4, a CMYK data generation unit 300 is a means for performing thestep S102 shown in FIG. 5. In the present embodiment, the CMYK datageneration unit 300 comprises a grid-point address generation unit 301and a CMYK calculation unit 302. The grid-point address generation unit301 is a counter generating indices (IDs) of grid points which arerepresentative points in a four-dimensional color space defined by fourCMYK color components. In the present embodiment where the number ofgrid points is 625, the grid-point address generation unit 301 countsfrom 0 to 624, and successively outputs each counted value as agrid-point ID. The CMYK calculation unit 302 calculates and outputs CMYKvalues corresponding to the grid-point ID. For example, in a case wherethe four-dimensional lookup table of the color conversion profiledivides each of the CMYK color components into 16, the CMYK values ofeach grid point are generated by a step of 16. Specifically,corresponding to the grid-point IDs=0, 1, 2, 3 . . . , CMYK data iscreated as follows.

[C,M,Y,K]=[0,0,0,0], [0,0,0,16], [0,0,0,32], [0,0,0,255], [0,0,16,0],[0,0,16,16], [0,0,16,32], . . . [0,0,16,255], . . . , . . . ,[255,255,255,0], [255,255,255,16], [255,255,255,32], . . .[255,255,255,255]

Besides, when this color conversion profile creating process isperformed by means of software using a computer, it is possible toretrieve CMYK data of one grid point from a preliminarily prepared listof CMYK data of all grid points.

A calorimetric value calculating unit (a calorimetric value convertingunit) 303 is a means for (performing a process equivalent to step S103shown in FIG. 5) converting the CMYK data of each grid point generatedin the CMYK calculation unit 302 into colorimetric values to be measuredwith respect to an image formed from the CMYK data by using the imageforming device 100. This converting process can utilize a calorimetricresult measured when the CMYK data of the grid point is output by theimage forming device 100, or can use a color estimation formula (usedfor calculating colorimetric values from CMYK data according to anapproximative function). A Lab value, an XYZ value, etc. can be used asthe calorimetric value. The present embodiment employs the Lab value asthe colorimetric value.

FIG. 5 shows step S101 as a procedure of obtaining the color estimationformula. A general method of constructing the color estimation formulais outputting a color patch by the image forming device 100 which is asource of CMYK data, measuring the color of the output patch by using aspectral calorimeter, and approximating a relationship between thecalorimetric data and output color data (=CMYK values) of the colorpatch. Such an operation of constructing the color estimation formula asabove is noting new, and can be performed manually, orsemiautomatically. When the procedure shown in FIG. 5 is performed bymeans of software using a computer, the operation of constructing thecolor estimation formula may be performed beforehand, which leaves onlya process of setting the color estimation formula to the step S101.

In order to improve reproducibility of a black character, it isnecessary to recognize whether or not the CMYK data represents ablack-character color. A black-character color judging unit 304 is ameans for performing this recognition (equivalent to step S108 shown inFIG. 5). Since the CMYK data of the color printer is processed asdescribed above such that a black character is reproduced solely by thecolor of K (black), it can be judged whether or not the CMYK datarepresents a black-character color by inspecting whether or not the CMYKdata consists solely of a black-character color. Specifically, theblack-character color judging unit 304 judges that the CMYK data doesrepresent a black-character color when the values of the CMYK data areas follows:C≦th, M≦th, Y≦th, and K>0

In these expressions, th is a predetermined threshold value, whichshould be as follows in the present embodiment.

th=0

A colorimetric value correction unit 305 performs a process (equivalentto step S104 shown in FIG. 5) of determining a manner of correcting thecolorimetric values according to a judgment result of theblack-character color judging unit 304 so as to correct the calorimetricvalues. Specifically, when the judgment result indicates that the CMYKdata represents a black-character color, the colorimetric valuecorrection unit 305 performs a contrast correction for emphasizing acontrast of the colorimetric values so as to improve reproducibility ofthe black character. When the judgment result does not indicate that theCMYK data represents a black-character color, the calorimetric valuecorrection unit 305 performs a contrast correction for subduing thecontrast of the calorimetric values so as to reproduce thenon-black-character color faithfully. In the present embodiment, thecalorimetric value correction unit 305 comprises a contrast conversiontable storage unit 306 and a calorimetric value correcting unit 307. Thecontrast conversion table storage unit 306 stores a contrast conversiontable used for a black-character color and a contrast conversion tableused for a non-black-character color. The calorimetric value correctingunit 307 uses either of the contrast conversion tables stored in thecontrast conversion table storage unit 306 selected according to thejudgment result of the black-character color judging unit 304 so as toperform the contrast correction to the calorimetric values.

A color conversion profile setting unit 309 uses colorimetric valuesL′a′b′ corrected by the calorimetric value correction unit 305 so as toset a color conversion profile used for converting the CMYK data intoRGB data. In the present embodiment, the color conversion profilesetting unit 309 comprises an Lab/RGB converting unit 310 and a colorconversion profile temporary storage unit 311. The Lab/RGB convertingunit 310 converts the calorimetric values L′a′b′ into RGB data. Thecolor conversion profile temporary storage unit 311 stores the convertedRGB data as the grid-point output values at addresses corresponding tothe grid-point IDs generated by the grid-point address generation unit301 into the form of a four-dimensional lookup table. The convertingprocess performed by the Lab/RGB converting unit 310 is equivalent tostep S105 shown in FIG. 5. The operation of storing the converted RGBdata in the color conversion profile temporary storage unit 311 isequivalent to step S106 shown in FIG. 5. The above-described colorconversion profile creating device repeats the steps S102 to S106including the step S108 for all of the grid points. In FIG. 5, thecompletion of this repetition is judged in step S107.

The color conversion profile thus created as the four-dimensional lookuptable in the color conversion profile temporary storage unit 311 iswritten to the color conversion profile storage unit 121 of the colorconverting device 104 of the present invention shown in FIG. 3 so thatthe CMYK data representing the black-character color is converted intothe RGB data with an emphasized contrast, as described with reference toFIG. 3.

Next, a description will be given, with reference to FIG. 6, of aspecific method of correcting the calorimetric values in thecolorimetric value correction unit 305. In FIG. 6, the axis of abscissasindicates a luminosity L before correction, and the axis of ordinatesindicates a luminosity L′ after correction. A solid line represents aninput-output relationship with respect to a black-character color, and adotted line represents an input-output relationship with respect to anon-black-character color. When the black-character color judging unit304 judges that the CMYK data represents a black-character color, thecalorimetric value correcting unit 307 corrects the calorimetric valuesLab to the calorimetric values L′a′b′ with an emphasized contrast bylinearly transforming a range [Bpt-Wp] of the luminosity L to a range[0-100], as indicated by the solid line. In FIG. 6, Wp is a white point(a luminosity when C=M=Y=K=0) of the CMYK data, which is generallyequivalent to a luminosity of a ground color. Bpt is a black point whichis equivalent to an output luminosity when C=M=Y=0 and K=255. On theother hand, when the black-character color judging unit 304 judges thatthe CMYK data represents a non-black-character color, the calorimetricvalue correcting unit 307 linearly transforms a range [0-Wp] of theluminosity L to the range [0-100], as indicated by the dotted line.Applying this contrast correction enables the creation of the colorconversion profile capable of reproducing a black character and anon-black character with a dynamic range appropriate for each thereof.

To describe further, since the above-mentioned contrast correctionlinearly transforms the luminosity of the white point of the CMYK datato 100, the ground color of a paper is transformed to a white color of adisplay so as to reproduce an image with an excellent visibility. Also,upon outputting from another color printer, no ink is applied to theground-color part; this not only saves ink, but also enables ahigh-quality color reproduction free from a rough surface. In addition,whereas the above-mentioned contrast correction transforms theluminosity L of a black-character color ([C,M,Y,K]=[0,0,0,255]) to theluminosity [L′=0], the contrast correction does not correct the blackpoint of a non-black-character color. Accordingly, a black character canbe reproduced with an excellent legibility due to an emphasizedcontrast. On the other hand, colors of parts other than a blackcharacter can be reproduced faithfully without impairing a gradation ina shadow area.

The contrast conversion table storage unit 306 stores the two types ofthe contrast conversion tables corresponding to the solid line and thedotted line shown in FIG. 6 as one-dimensional lookup tables, and thecalorimetric value correcting unit 307 can select and use either of thecontrast conversion tables according to the black-character colorjudgment result. However, the present invention is not limited thereto.That is, since the conversion of the calorimetric values only requiresthe values of the white point Wp and the black point Bpt, the contrastconversion table storage unit 306 may only store the values of the whitepoint Wp and the black point Bpt such that the calorimetric valuecorrecting unit 307 selects the stored value of Bpt when the CMYK datarepresents a black-character color, whereas the calorimetric valuecorrecting unit 307 selects 0 as the value of Bpt when the CMYK datarepresents a non-black-character color so as to perform the lineartransformations with respective dynamic ranges in the contrastcorrection.

Additionally, since a K ink used in such an apparatus as a color printersometimes assumes some color, the relationship a=b=0 sometimes does notstand as to the calorimetric values Lab of the CMYK data correspondingto a black-character color. In this case, simply making the luminosityL′ of the black-character color zero does not cause the relationship[L′,a′,b′]=[0,0,0] to stand, which makes the CMYK data aninexistent-color signal that is possibly unable to be converted into RGBdata. In order to solve this problem, it is effective to forcibly makethe CMYK data an achromatic-color signal.

Thereupon, in another embodiment, with respect to a black-charactercolor, the colorimetric value correcting unit 307 converts thecalorimetric values Lab into [L′,0,0] so as to make a chroma thereofzero. This is also one of features of the present invention. Performingthis forcible achromatizing process enables a high-quality reproductionof a black character even when a K ink assuming some color is used inthe color printer 101. This also applies to the following embodiment.

[Second Embodiment of the Color Converting Device 104]

In the first embodiment of the color converting device 104 describedwith reference to FIG. 3, the input CMYK data is a signal representingeach of the colors in 8 bits (generally referred to as a multivaluedsignal)

FIG. 7 is a block diagram of a second embodiment of the color convertingdevice 104 for performing a color conversion of CMYK data binarized in adither process. The color converting device 104 according to the presentembodiment comprises buffer memories 125 c, 125 m, 125 y and 125 kcorresponding to the CMYK color components, respectively, andbinary/multivalued conversion units 126 c, 126 m, 126 y and 126 k, inaddition to the color converting unit 120 and the color conversionprofile storage unit 121 shown in FIG. 3. This color converting device104 operates as follows.

A predetermined number of consecutive pixels of input binary CMYK dataare temporarily stored in the buffer memories 125 c, 125 m, 125 y and125 k corresponding to the color components, respectively. The binaryCMYK data temporarily stored therein is successively supplied to thecorresponding binary/multivalued conversion units 126 c, 126 m, 126 yand 126 k. The binary/multivalued conversion units 126 c, 126 m, 126 yand 126 k first replace “0” of the binary CMYK data with an 8-bit signalvalued “0”, or replace “1” of the binary CMYK data with an 8-bit signalvalued “255”, and then perform a smoothing filtering process to this8-bit signal so as to generate CMYK data representing each of the colorsin 8 bits and transmit the CMYK data to the color converting unit 120.

The color converting unit 120 operates in the same manner as in theabove-described first embodiment. However, the contents of the colorconversion profile (the four-dimensional lookup table) stored in thecolor conversion profile storage unit 121 are different from the firstembodiment. Descriptions will be given, with reference to FIG. 8 andFIG. 9, of these different points.

Since the binary/multivalued conversion units 126 c, 126 m, 126 y and126 k perform the above-mentioned smoothing filtering process,high-frequency components of the binary CMYK data are removed. As aresult of this, especially character parts become obscure so as todeteriorate a legibility thereof, which makes small-sized charactersdifficult to read. A description will be given, with reference to FIG.8, of this phenomenon.

FIG. 8A and FIG. 8B illustrate changes in pixel values due to thesmoothing filtering process performed to the binary CMYK data. FIG. 8Aillustrates changes in pixel values in the vicinity of a blackcharacter. FIG. 8B illustrates changes in pixel values in a pictorialpart. To simplify the illustrations, FIG. 8A and FIG. 8B show only fivepixels in a horizontal direction. Graphs at the left side of arrows inFIG. 8A and FIG. 8B show pixel values of the binary CMYK data before thesmoothing filtering process. Graphs at the right side of the arrows inFIG. 8A and FIG. 8B show pixel values of the 8-bit CMYK data after thesmoothing filtering process. However, for the purpose of equalizinglevels of the binary CMYK data and the 8-bit CMYK data, the graphs show“1” of the binary CMYK data and “255” of the 8-bit CMYK data at the sameheight.

In the left-side graphs shown in FIG. 8A, a black-character pixel([C,M,Y,K]=[0,0,0,1]) is present at the center. Pixels around the blackcharacter are assumed to be paperwhite, each of which is[C,M,Y,K]=[0,0,0,1]. The 8-bit CMYK data obtained by performing thesmoothing filtering process to the binary CMYK data represented in theleft-side graphs has a decreased value for the black-character pixel,and has an increased density for an image consisting of the pixelsaround the black character, as shown in the right-side graphs shown inFIG. 8A. Thereby, the black character becomes dim.

In FIG. 8B, the right-side graphs show pixel values of the 8-bit CMYKdata obtained by performing the smoothing filtering process to thebinary CMYK data represented in the left-side graphs. The binary CMYKdata binarized by a dither process has such a characteristic that CMYKinks are applied at intervals. Multivalued CMYK data before the ditherprocess which represents the pictorial part does not contain plenty ofhigh-frequency components. Accordingly, the 8-bit CMYK data obtained byperforming the smoothing filtering process to the binary CMYK datamerely returns to a state (of the multivalued CMYK data) before thedither process. Therefore, the smoothing filtering process does notdeteriorate the pictorial parts very much, compared to character parts.

Thereupon, in the present embodiment, in the course of the colorconversion profile creating device shown in FIG. 4 creating the colorconversion profile to be stored in the color conversion profile storageunit 121, the colorimetric value correction unit 305 performs anonlinear contrast conversion only to a black-character color so as toemphasize the contrast of the black character intensively. Using thecolor conversion profile thus formed largely enhances thereproducibility of a black-character part which tends to become obscuredue to the smoothing filtering process. However, performing thenonlinear contrast conversion to pictorial parts other than charactersgreatly changes the colors of the pictorial parts. Therefore, the samelinear contrast conversion as in the first embodiment is applied to thepictorial parts.

In addition, also in the course of creating the color conversion profileaccording to the present embodiment, the black-character color judgingunit 304 can judge whether or not the CMYK data represents ablack-character color in the same manner as described above in the firstembodiment. However, if even only one color pixel exists in the vicinityof a black character, the relationship C=M=Y=0 does not stand.Thereupon, using nonzero values (e.g., 16) as the above-mentionedjudgment threshold value th can prevent this undesired recognition. As amatter of fact, since the black character is often drawn on a whitebackground or on a highlighted color, a black-character color and anon-black-character color can be distinguishingly recognized with highprecision even by judging as above only from a balance of C, M, Y and K.

A description will be given, with reference to FIG. 9, of a specificexample of the nonlinear contrast conversion performed for the purposeof creating the color conversion profile used in the present embodiment.In FIG. 9, the axis of abscissas indicates a luminosity L beforecorrection, and the axis of ordinates indicates a luminosity L′ aftercorrection, as in FIG. 6. A solid line represents an input-outputrelationship with respect to a black-character color, and a dotted linerepresents an input-output relationship with respect to anon-black-character color, also as in FIG. 6. The input-outputrelationship with respect to the non-black-character color is the sameas in FIG. 6.

With respect to the black-character color, the calorimetric valuecorrecting unit 307 intensively emphasizes the contrast of the blackcharacter by nonlinearly transforming a range [Bpt-Wp] of the luminosityL to a range [0-100], as indicated by the solid line. A color conversionperformed by using the color conversion profile created by theabove-described correction largely emphasizes the contrast of theblack-character part. Accordingly, a character dimmed due to thesmoothing filtering process can be restored to a considerably legibleRGB image.

Besides, with respect to multivalued CMYK data, too, it is effective tointensively emphasizes the contrast of a black character by performingthe nonlinear transformation shown in FIG. 9, depending oncharacteristics thereof.

[Third Embodiment of the Color Converting Device 104]

FIG. 10 is a block diagram of a third embodiment of the color convertingdevice 104. The color converting device 104 according to the presentembodiment comprises a data buffer 150, a black-character color judgingunit 151, a contrast conversion table storage unit 152, aCMYK/colorimetric-value conversion unit 153, a calorimetric valuecorrection unit 154, and a colorimetric-value/RGB conversion unit 155.

The CMYK data supplied from the image forming device 100 is temporarilystored in the data buffer 150, and is successively supplied to theblack-character color judging unit 151 and the CMYK/colorimetric-valueconversion unit 153. The black-character color judging unit 151 is ameans for judging whether or not the CMYK data represents ablack-character color in the same manner as the black-character colorjudging unit 304. The contrast conversion table storage unit 152 storescontrast conversion tables used for a black-character color and anon-black character color as shown in FIG. 6 (or FIG. 9). Either of thecontrast conversion tables is selected according to a judgment result ofthe black-character color judging unit 151.

The CMYK/colorimetric-value conversion unit 153 converts the CMYK datainto calorimetric values (Lab values in the present embodiment) of theimage forming device 100 in the same manner as does the colorimetricvalue calculating unit 303 shown in FIG. 4, and supplies thecalorimetric values to the calorimetric value correction unit 154. Thecalorimetric value correction unit 154 uses either of the contrastconversion tables stored in the contrast conversion table storage unit152 selected according to the black-character color judgment result soas to perform the same contrast correction to the colorimetric valuesLab as does the colorimetric value correcting unit 307 shown in FIG. 4,and outputs corrected colorimetric values L′a′b′.

Additionally, as described in relation to the calorimetric valuecorrecting unit 307, in case a K ink used in such an apparatus as acolor printer assumes some color, the calorimetric value correction unit154 may convert the colorimetric values Lab of the CMYK datacorresponding to a black-character color into [L′,0,0] so as to forciblyachromatize the calorimetric values L′a′b′.

The colorimetric-value/RGB conversion unit 155 converts the calorimetricvalues L′a′b′ corrected by the calorimetric value correction unit 154into an RGB color signal.

It is evident that the above-described configuration enables a colorconversion of the CMYK data into the RGB data which is equivalent to theabove-described first embodiment.

Besides, though not shown in FIG. 10, the color converting device 104according to the present third embodiment may further comprise meansequivalent to the binary/multivalued conversion units 126 c, 126 m, 126y and 126 k shown in FIG. 7 at an input side or an output side, whereinthe contrast conversion table storage unit 152 stores a nonlinearcontrast conversion table corresponding to the solid line shown in FIG.9 used for a black-character color. As evident from the abovedescription, the color converting device 104 having the above-describedstructure can generate RGB data with an excellent black-characterreproducibility from the CMYK data binarized by such a process as adither process, as in the second embodiment.

[Description of the Image Forming Device 100: as a Color CopyingMachine]

FIG. 11 is a block diagram of a configuration of a color copyingmachine. A description will be given, with reference to FIG. 11, ofoperations of generating the CMYK data, and structures related thereto,when the image forming device 100 is a color copying machine.

In FIG. 11, an image input device (a scanner) 401 reads an image of asubject copy, and supplies RGB data. Since the RGB data is linear toreflectance, a Log transformation circuit 402 transforms the RGB datainto data substantially linear to a density of the image by performing alogarithm transformation, and supplies the logarithm-transformed data toa filter circuit 403, an edge separation circuit 407, a dot separationcircuit 408, and a color separation circuit 409. The circuits 407, 408and 409 are provided for performing an image area separation process. Ajudge circuit 410 comprehensively judges separation results obtained bythe circuits 407, 408 and 409, and classifies the separation resultsinto image areas such as a black-character area, a photograph area, adot area. For example, the separation result of the edge separationcircuit 407 indicates “edge”, and the separation result of the colorseparation circuit 409 indicates “black pixel”, the judge circuit 410judges that the separation results together indicate “black character”.The judge circuit 410 supplies this image area separation result to thefilter circuit 403, a color correction circuit 404, a UCR circuit 405,and a dither circuit 406. The filter circuit 403 subjects thelogarithm-transformed data to a filtering process that suits the imagearea, and then the color correction circuit 404 subjects the filtereddata to a color correction that suits the image area so as to generateCMYK data. The color correction circuit 404 supplies the CMYK data tothe UCR circuit 405. The UCR circuit 405 subjects the CMYK data to a UCR(undercolor separation) process that suits the image area, and suppliesthe UCR-processed CMYK data to the dither circuit 406. The dithercircuit 406 subjects the UCR-processed CMYK data to a dither processusing a dither matrix that suits the image area, and supplies thedither-processed CMYK data to an image output device 414 (animage-forming engine of a laser printer, etc.). The image output device414 prints out the dither-processed CMYK data.

In the above-described course, the image area separation process isperformed by judging a local characteristic of an image. Therefore,accurately speaking, pixels in the vicinity of edges of a blackcharacter are judged to be black characters. As to a small-size blackcharacter, the black character is consequently judged to be a blackcharacter as a whole. However, as to a large-size black character suchas in a title, only edge pixels of the black character are judged to beblack characters while interior pixels of the character are recognizedas photographs. Accordingly, the pixels judged as black characters areconverted into monochromatic K data having pixel levels according to theintensity of edges in the color correction and the UCR process so as tobe printed solely by an K ink. However, the pixels judged as photographsor dots are converted into four-color CMYK data so as to be printed byoverlapping the four-color inks. Accordingly, as illustratively shown inFIG. 12, as to a large-size black character, only edge parts of theblack character are reproduced monochromatically by the K color, andinterior parts of the character are reproduced by the four CMYK colors.It is noted that a recent color copying machine adjusts density levelsof the edge parts and the interior parts so as to prevent the edge partsfrom appearing unnatural.

When an CMYK image, such as a large-size character as mentioned above,consists of a monochromatic K part and a four-color overlapped partadjacent to each other, converting the CMYK image into RGB data withdifferent contrasts for the monochromatic K part and other parts, as inthe color converting device 104 according to the first or thirdembodiment, may possibly make a resulting image seem unnatural with ablack character being fringed, when the RGB data is displayed on thedisplay 103 or is printed out from the color printer 101. On the otherhand, subjecting a small-size character to the contrast emphasis yieldsan increased reproducibility when the small-size character is outputfrom the (other) color printer 101. Hereinbelow, a description will begiven of an embodiment of the color converting device 104 devised inconsideration of this point.

[Fourth Embodiment of the Color Converting Device 104]

FIG. 13 is a block diagram of a fourth embodiment of the colorconverting device 104. The color converting device 104 according to thepresent embodiment is supplied with the CMYK data from, for example, theUCR circuit 405 of the color copying machine via a storage device 415,as shown in FIG. 11. It is noted that the present invention encompassesthe color copying machine incorporating the color converting device 104of the present embodiment internally connected as shown in FIG. 11.Likewise, the present invention also encompasses the image formingdevice, such as a color printer, incorporating the color convertingdevice 104 of the first, second or third embodiment.

In FIG. 13 in which the elements 150 to 155 are the same elements asshown in FIG. 10, the color converting device 104 further comprises onlya non-black-character color judging unit 160 and a comprehensive judgeunit 161. The CMYK data (representing each of the colors in 8 bits, forexample) supplied from the color copying machine is temporarily storedin the data buffer 150. At the same time when CMYK data of pixels ofinterest is supplied from the data buffer 150 to theCMYK/colorimetric-value conversion unit 153, CMYK data in the vicinityof the pixels of interest is supplied to the non-black-character colorjudging unit 160. The non-black-character color judging unit 160 judgeswhether or not there exists a non-black-character color pixel of a lowluminosity in the vicinity of the pixels of interest. For instance, thenon-black-character color judging unit 160 examines CMYK data of pixelsexcept the pixels of interest within an 8×8 pixel field centered aroundthe pixels of interest, and when either of chromatic values of C, M, andY exceeds a predetermined value, the non-black-character color judgingunit 160 judges that there exists a non-black-character color pixel of alow luminosity in the vicinity of the pixels of interest. This judgmentresult and the judgment result of the black-character color judging unit151 are supplied to the comprehensive judge unit 161. The comprehensivejudge unit 161 judges that the pixels of interest represent ablack-character color, only when the black-character color judging unit151 judges that the pixels of interest represent a black-charactercolor, and the non-black-character color judging unit 160 judges thatthere does not exist a non-black-character color pixel of a lowluminosity in the vicinity of the pixels of interest. According to thiscomprehensive judgment result, the comprehensive judge unit 161 selectsthe contrast conversion table used for a black-character color stored inthe contrast conversion table storage unit 152. In other words, wheneverthe non-black-character color judging unit 160 judges that there existsa non-black-character color pixel of a low luminosity in the vicinity ofthe pixels of interest, the calorimetric value correction unit 154performs a contrast correction using the contrast conversion table usedfor a non-black-character color. Besides, when the calorimetric valuecorrection unit 154 performs a contrast correction using the contrastconversion table used for a black-character color, the calorimetricvalue correction unit 154 may forcibly achromatize the colorimetricvalues L′a′b′. The present invention encompasses the color convertingdevice thus forcibly achromatizing the calorimetric values.

According to the present embodiment, supplying RGB data from the colorconverting device 104 to the computer 102 so as to display on thedisplay 103 or print out from the color printer 101 can prevent theoccurrence of a fringing (a pseudo outlining) of a large-size blackcharacter, which is described with reference to FIG. 12, so as to enablea high-quality black-character reproduction.

Additionally, the judgment result of the black-character color judgingunit 151 and the judgment result of the non-black-character colorjudging unit 160 may be supplied directly to the calorimetric valuecorrection unit 154, and the calorimetric value correction unit 154 mayselect either of the contrast conversion tables according to thejudgment results.

[Embodiment of the Present Invention Using a Computer]

As mentioned above, the present invention can be embodied by means ofsoftware in a computer in general or in an image forming device.

For example, loading the color conversion profile (the four-dimensionallookup table) stored in the color conversion profile storage unit 121shown in FIG. 3 on a memory of a computer or an image forming device,and executing a program including a step corresponding to the grid-pointaddress generation unit 123 and a step corresponding to theinterpolative calculation unit 124 can realize a color converting deviceequivalent to the color converting device 104 having the structure shownin FIG. 3, or the color conversion process thereof. In this case, theprogram is to further include a step corresponding to thebinary/multivalued conversion units 126 c, 126 m, 126 y and 126 k, and,if necessary, a step for controlling a buffering using the buffermemories 125 c, 125 m, 125 y and 125 k reserved on the memory for thatpurpose.

Similarly, the color converting device 104 having the structure shown inFIG. 10 or FIG. 13 or the color conversion process thereof can berealized by means of software. This involves loading the contrastconversion table stored in the contrast conversion table storage unit152 on a memory, and executing a program including steps correspondingto the functional elements (151, 153, 154, 155, 160 and 161) shown inFIG. 10 or FIG. 13, and, if necessary, a step for controlling abuffering using the data buffer 150 reserved on the memory for thatpurpose.

In addition, the color conversion profile creating device shown in FIG.4 or the color conversion profile creating process thereof can berealized by means of software. A program therefor includes stepscorresponding to the units 300, 303, 304, 305, and 310 shown in FIG. 4,and a step of storing the RGB data converted into by the Lab/RGBconverting unit 310 in a four-dimensional lookup table on a memory.

The present invention encompasses the above-described programs. Thepresent invention also embraces various recording mediums, such as amagnetic disk, an optical disk, a magneto-optical disk and asemiconductor memory device, storing the above-described programs.

Although the above-described embodiments use the RGB data as outputcolor data, it is evident from the above descriptions that the presentinvention is applicable to cases using output color data in anotherformat.

[Fifth Embodiment of a Color Converting Device: as a Computer 502]

[Configuration of an Image Processing System]

FIG. 14 is a schematic diagram of another embodiment of an imageprocessing system according to the present invention. In FIG. 14, theimage processing system comprises image forming devices 500 and 501, acomputer 502, a display 503, and a printer controlling device 504.

The image forming device 500 (P1) supplies CMYK image data to anexternal device. Specifically, the image forming device 500 is a colorprinter, a color copying machine or a color facsimile device comprisinga data storage device, such as a hard disk or a RAM.

The computer 502 has functions such as a color converting function forconverting the CMYK image data supplied from the image forming device500 (P1) into RGB image data. Software including various applicationsand printer drivers can be installed into the computer 502. The computer502 can display the RGB image data on the display 503. The computer 502can also cause the RGB image data to be printed by the image formingdevice 501 (P2) by activating a printer driver corresponding to theimage forming device 501 (P2).

The image forming device 501 (P2) receives drawing data from thecomputer 502, and outputs a hard copy thereof. This image forming device501 (P2) is a device such as a color printer comprising the printercontrolling device 504. The printer controlling device 504 is aprocessor for converting the drawing data transmitted from the computer502 into image data to be printed as a hardcopy. The printer controllingdevice 504 comprises a rendering unit, a band buffer, a color convertingunit, a gradating unit, and a page memory, etc.

Besides, although the printer controlling device 504 is described in thepresent embodiment as being provided in the image forming device 501(P2), the printer controlling device 504 may be provided as a deviceindependent from the image forming device 501 (P2). Further, part offunctions of the printer controlling device 504 may be taken over by theprinter driver of the computer 502, etc.

[Operations of the Image Processing System]

Next, a description will be given of operations as a whole of theabove-mentioned image processing system shown in FIG. 14. First, theimage forming device 500 (P1) stores CMYK image data generated in thecourse of outputting a hard copy, in the built-in hard disk. Anoperation of outputting a hard copy means a printing operation using acolor printer or a copying operation using a color copying machine, forexample. The CMYK image data generated in the image forming device 500(P1) is transferred to the computer 502 via a network. The computer 502performs a color conversion converting the transferred CMYK image datainto RGB image data, and retains the RGB image data in a storage mediumsuch as a hard disk provided in the computer 502.

An operator of the computer 502 can view the RGB image data bydisplaying the RGB image data stored in the computer 502 on the display503 as occasion arises, can process the RGB image data, and can supplythe RGB image data to a different image forming device (501) so as tohave the RGB data printed.

[Description of a Color Converting Method]

In the above-described image processing system, the computer 502performs a color converting operation for converting four-dimensionaldata of a CMYK signal into three-dimensional data, such as an RGBsignal. In the present embodiment, the color converting operation forconverting the four-dimensional data is performed by utilizing afour-dimensional memory map interpolative calculation.

Then, a description will be given of a principle of a memory mapinterpolating method according to the present embodiment performed forinterpolating four-dimensional data. The four-dimensional memory mapinterpolative calculation method divides a four-dimensional color spacehaving four axes representing four signals of C, M, Y and K into aplurality of 16-vertex units, and performs an interpolative calculationby using interpolation parameters assigned to a 16-vertex unit to whichan input signal belongs.

Here, a specific description will be given of an instance where each ofthe signals of C, M, Y and K is 8-bit data, and each of the axes isdivided into 15 (a four-dimensional color space defined by the four axesis divided into 15⁴ 16-vertex units). Dividing the 8-bit data into 15makes one step 17 (=255/15). Thereupon, assuming Tp=T/17 and ΔT=17 (T iseach of color signal values C, M, Y and K; Tp and ΔT are integralvalues), the input signal (X), being divided into higher-order data andlower-order data, is represented as (C=17*Cp+ΔC, M=17*Mp+ΔM, Y=17*Yp+ΔY,K=17*Kp+ΔK).

Coordinates of the vertices (grid points) of a 16-vertex unitsurrounding the input signal X are as follows:

[C, M, Y, K]=[17*Cp, 17*Mp, 17*Yp, 17*Kp], [17*Cp, 17*Mp, 17*Yp,17*(Kp+1)], [17*(Cp+1), 17*Mp, 17*Yp, 17*Kp], [17*(Cp+1), 17*Mp, 17*Yp,17*(Kp+1)], [17*Cp, 17*(Mp+1), 17*Yp, 17*Kp], [17*Cp, 17*(Mp+1), 17*Yp,17*(Kp+1)], [17*Cp, 17*Mp, 17*(Yp+1), 17*Kp], [17*Cp, 17*Mp, 17*(Yp+1),17*(Kp+1)], [17*(Cp+1), 17*(Mp+1), 17*Yp, 17*Kp], [17*(Cp+1), 17*(Mp+1),17*Yp, 17*(Kp+1)], [17*(Cp+1), 17*Mp, 17*(Yp+1), 17*Kp], [17*(Cp+1),17*Mp, 17*(Yp+1), 17*(Kp+1)], [17*Cp, 17*(Mp+1), 17*(Yp+1), 17*Kp],[17*Cp, 17*(Mp+1), 17*(Yp+1), 17*(Kp+1)], [17*(Cp+1), 17*(Mp+1),17*(Yp+1), 17*Kp], [17*(Cp+1), 17*(Mp+1), 17*(Yp+1), 17*(Kp+1)]

FIG. 15 shows this 16-vertex unit conveniently divided into twothree-dimensional cubes despite its original form of a four-dimensionalsolid, because the four-dimensional solid is unable to be figured. Thatis, the left cube is an interpolation unit of C-M-Y with the value Kbeing fixed at Kp×Δ, and the right cube is an interpolation unit ofC-M-Y with the grid point of K being fixed at (Kp+1)×Δ (Δ is a grid sizeof the interpolation unit; Δ=17 when the 8-bit data is divided into 15).

One of publicly known methods for interpolating this 16-vertex unit is afive-point interpolation method which divides the 16-vertex unit into 24five-vertex solids so as to perform a five-point interpolativecalculation. However, since there are as many as 24 patterns ofselecting five points, determining a five-vertex solid requires acomplicated judgment. Thereupon, the present embodiment divides the16-vertex unit into six 8-vertex solids (T1 to T6) as shown in FIG. 16so as to adopt an eight-point interpolative calculation.

First, a 16-vertex unit is selected from a plurality of the 16-vertexunits according to the higher-order data of the input color signals.Next, in the eight-point interpolative calculation, the lower-order dataΔC, ΔM and ΔY of the input color signals C, M and Y are compared witheach other in terms of values (magnitude relation: large or small) so asto determine (select) an 8-vertex solid from among the six 8-vertexsolids. FIG. 17 shows expressions used in this comparison.

Subsequently, an interpolative calculation process is performed by usingthe 8-vertex solid selected in the 8-vertex solid determining processdescribed above. Here, a description will be given, with reference toFIG. 18, of an interpolative calculation method, in a case where the8-vertex solid T1 is selected. FIG. 18 shows the selected 8-vertex solidT1. First, in the interpolative calculation method according to thepresent embodiment, two corresponding vertices of the 8-vertex solid arelinearly interpolated so as to form a tetrahedron. In the example shownin FIG. 18, Pa, Pb, Pc and Pd are calculated as follows.Pa=P0+(P8−P0)×Δk  (Expression 1-a)Pb=P1+(P9−P1)×Δk  (Expression 1-b)Pc=P3+(P11−P3)×Δk  (Expression 1-c)Pd=P7+(P15−P7)×Δk  (Expression 1-d)

In these expressions, Δk is expressed as Δk=ΔK/Δ(0≦Δk≦1.0), and Pi meansan output value assigned to each vertex. Thus, interpolating thecorresponding two vertices linearly by using the lower-order data of thecolor signal K can replace a four-dimensional interpolative calculationwith a three-dimensional tetrahedral interpolative calculation.

After the formation of the tetrahedrons, an output value P can becalculated in the same manner as in a normal tetrahedral interpolativecalculation with a three-dimensional space, as follows. $\begin{matrix}\begin{matrix}{P = {{{\alpha\Delta}\quad{C/\Delta}} + {{\beta\Delta}\quad{M/\Delta}} + {{\gamma\Delta}\quad{Y/\Delta}} + \delta}} \\{= {{\left( {{Pb} - {Pa}} \right)\quad\Delta\quad{C/\Delta}} + {\left( {{Pc} - {Pb}} \right)\quad\Delta\quad{M/\Delta}} +}} \\{{{\left( {{Pd} - {Pc}} \right)\quad\Delta\quad{Y/\Delta}} + {Pa}}\quad}\end{matrix} & \begin{matrix}\left( {{Expression}\quad 2\text{-}a} \right) \\\left( {{Expression}\quad 2\text{-}b} \right)\end{matrix}\end{matrix}$

In cases where the 8-vertex solids T2 to T6 are selected, basically thesame interpolative calculation method is performed. FIG. 19 showscorrespondences between the 8-vertex solids T1 to T6 and thecoefficients α, β, γ and δ used in the expressions above. In FIG. 19,P(i,j) represents a value obtained by linearly interpolating outputvalues assigned to vertices Pi and Pj by Δk.

In the present embodiment, the four-dimensional interpolativecalculation is performed by the expressions above. Besides, althoughFIG. 15 shows the 16-vertex unit (an interpolation object space) dividedinto the two cubes, the interpolation object space of the presentinvention is not limited thereto; the present invention is applicable toa 16-vertex solid having edges different in length, and to atransformational 16-vertex solid corresponding to an input signalrepresented by polar coordinates, etc.

[Description of a Color Converting Device]

Hereinbelow, a description will be given of a specific example of acolor converting device realizing the above-described color convertingmethod. In the image processing system shown in FIG. 14, the computer502 controls the system so as to convert CMYK image data transmittedfrom the image forming device 500 (P1) into RGB image data. FIG. 20 is ablock diagram of an example of the computer 502 performing the colorconverting operation. The computer 502 comprises a network interfacecard (NIC) communicating data with an external device, a disk (DISK)temporarily storing image data transmitted from the NIC, afour-dimensional lookup table (4D-LUT) storage unit (storing means), acentral processing unit (CPU: determining means, reading means,generating means, interpolating means) performing a color convertingprocess, and a random access memory (RAM).

First, when image data is transmitted to the computer 502 via the NIC,the image data is temporarily retained in the DISK. Next, the CPUretrieves the image data from the DISK, and stores the image data in theRAM. Then, the CPU performs a color converting process while accessingthe RAM. To perform the color converting process, the CPU reads theimage data, pixel by pixel, from the RAM, and evaluates CMYK values ofthe read pixel so as to determine a read address in the 4D-LUT storageunit. Then, after reading therefrom interpolation parameters necessaryfor an interpolative calculation, the CPU performs a color conversionconverting the pixel data into such a signal as an RGB signal. The CPUperforms such color conversions while successively reading pixel datafrom the RAM, and retains the conversion results (such as the RGBsignals) in the DISK. Upon completion of the color conversions for allthe CMYK image data retained in the DISK, the image data is transferredto an external device via the NIC.

A description will be given, with reference to FIG. 21, of the colorconverting operation performed by the CPU. FIG. 21 is a flowchart of thecolor converting operation (the interpolative calculation process).First, in step S151 (determining means; determining step), it is judged(determined) which of the 8-vertex solids corresponds to input imagedata. FIG. 22 is a flowchart of this 8-vertex solid judging(determining) process. As shown in FIG. 22, in the present invention, ajudging process imposing a heavy load on a CPU is performed only withthe lower-order data (ΔC, ΔM and ΔY) of the three input signals C, M andY, and thus can be performed only with three steps at the maximum asshown in FIG. 22.

After the 8-vertex solid is determined, interpolation parameters areread from the 4D-LUT storage unit, in step S152 (reading means). Thiscolor converting operation (the interpolative calculation process)requires the parameters shown in FIG. 19. The addressing of the 4D-LUTstorage unit is performed according to the higher-order data Cp, Mp, Ypand Kp of the input signals C, M, Y and K, and to the determinationresult of the 8-vertex solid, as described in detail later herein. Afterthe parameters corresponding to the 8 vertices are read, P(i,j) iscalculated, in step S153 (generating means; generating step). Then, instep S154 (interpolating means; interpolating step), thethree-dimensional interpolative calculation is performed so as tocalculate a value of the output RGB signal.

[Method of Reading Parameters From the 4D-LUT Storage Unit]

A description will be given of a method of reading the interpolationparameters from the 4D-LUT storage unit. The 4D-LUT storage unit storesoutput values corresponding to four-dimensional divisional grid points.For example, when each of input CMYK data of C, M, Y and K is dividedinto 15, the 4D-LUT storage unit successively stores the followingoutput values corresponding to the CMYK data.

[C,M,Y,K]=[0,0,0,0], [0,0,0,15], [0,0,0,30], . . . [0,0,0,255],[0,0,15,0], [0,0,15,15], [0,0,15,30], . . . [0,0,15,255], . . . , . . ., [255,255,255,0], [255,255,255,15], [255,255,255,30], . . .[255,255,255,255]

When the 4D-LUT storage (memory) unit stores the parameters in thisorder, parameters of [C,M,Y,K]=[c,m,y,k] and [c,m,y,k+Δ] are alwayslocated at serial addresses. Thus, since the 4D-LUT storage unitserially stores parameters necessary for performing the linearinterpolative calculations represented by the expressions 1, the CPU canretrieve two parameters simultaneously by one memory access.Accordingly, the CPU can read the parameters at high speed.

For example, when the CPU reads color conversion parameters used inrelation to the above-mentioned 8-vertex solid T1, the CPU can retrievetwo bytes at the same time because P1 and P9 are serially located.Similarly, the CPU can simultaneously retrieve P0 and P8, P3 and P11,and P7 and P15, respectively. Accordingly, the CPU needs to access the4D-LUT storage unit only four times.

As described above, in the present embodiment, the simple 8-vertex solidjudging (determining) process and the fast memory access enable thecolor conversion appropriate for a CPU processing.

Further, each of the expressions 1 calculates a sum of products. Some ofrecent CPUs are capable of performing such a sum-of-products calculationin one clock, or capable of calculating a plurality of sum-of-productscalculations in parallel. In consideration of this trend, performing thesum-of-products calculations represented by the expressions 1 does notcause a problem in terms of a processing rate. However, in case the CPUis inapt to performing the sum-of-products calculation, the load of thesum-of-products calculations offsets the advantage of theabove-described simple judging (determining) process.

Thereupon, in case the CPU is incapable of accelerating thesum-of-products calculation, the multiplication terms in the expression1 may be replaced with memory lookup operations. For example, as to theexpression 1-a, retaining a correspondence of the differential value(P8-P0) and Δk with a multiplication result thereof in a static memoryenables the memory lookup operation to replace the multiplication.

Since ΔK is the lower-order data of the K signal, ΔK only assumes valuesin a limited range. For example, when each of the input CMYK data isdivided into 15, ΔK only assumes 17 patterns of values. Additionally,the differential value (P8-P0) does not claim more than 8 bits.Accordingly, the above-mentioned multiplication only requires amultiplication memory of a size as small as 4.25 Kbytes (=256 bytes×17),which does not impose a load on the CPU processing. In addition, thesame multiplication memory can be used in performing the expressions 2.In this case, multiplications in the interpolative calculation are notnecessary. Therefore, performing the 8-vertex solid judging(determining) process at high speed in the CPU processing can enhancethe performance of the interpolative calculation as a whole.

[Sixth Embodiment of a Color Converting Device]

In the above-described fifth embodiment, the 16-vertex unit is dividedinto the six 8-vertex solids so as to perform the three-dimensionaltetrahedral interpolative calculation by utilizing the linearinterpolative calculations. In the present sixth embodiment, based onthe same concept, the 16-vertex unit is divided into the two 12-vertexsolids.

FIG. 23 illustrates the two 12-vertex solids divided from the 16-vertexunit. In FIG. 23, each of the two 12-vertex solids is divided intotriangular prisms. In this case, a 12-vertex solid judging (determining)process needs to be performed only once because only two of thelower-order data ΔC, ΔM, ΔY and ΔK of the four signals C, M and Y arecompared with each other, unlike the 8-vertex solid judging(determining) process.

An interpolative calculation for the 12-vertex solid is similar to theinterpolative calculation for the 8-vertex solid described above in thefifth embodiment. That is, two corresponding vertices of the 12-vertexsolid are linearly interpolated by the lower-order data of the K signalso as to form a three-dimensional triangular prism, and thereafter, anormal triangular-prism interpolative calculation is performed.

[Seventh Embodiment of a Color Converting Device]

Whereas the above-described fifth and sixth embodiments are realized asthe processes of the CPU, the present embodiment can be realized bymeans of hardware. FIG. 24 is a block diagram of an example of thepresent invention realized by means of hardware. In the presentembodiment, the expression 2-b is transformed so as to simplify acircuit.

That is, in the expression 2-b(P=(Pb−Pa)ΔC/Δ+(Pc−Pb)ΔM/A+(Pd−Pc)ΔY/Δ+Pa), (Pb−Pa) can be transformedas follows, by using the expressions 1.Pb−Pa=P1+(P9−P1)×Δk−P0−(P8−P0)×Δk=P1−P0+(P9−P1−P8+P0)×Δk=(P1−P0)+((P9−P8)−(P1−P0))Δk

At this point, assuming a=P1−P0 and a′=P9−P8 and storing (a) and (a′) ina 4D-LUT enables an interpolative calculation to be performed bymultiplying each of ΔC, ΔM and ΔY by a simple sum of products, as shownin FIG. 24.

Similarly, in the expression 2-b, (Pc−Pb), (Pd−Pc) and Pa can betransformed as follows, by using the expressions 1.Pc−Pb=(P3−P1)+((P11−P9)−(P3−P1))Δk Pd−Pc=(P7−P3)+((P15−P11)−(P7−P3))ΔkPa=P0+(P8−P0)×Δk

Accordingly, the expression 2-b is generalized as follows.P=((a′−a)ΔK+a)ΔC+((b′−b)ΔK+b)ΔM+((c′−c)ΔK+c)ΔY+(d′−d)ΔK+d

Since a, a′, b, b′, c and c′ have different values for each of 6-vertexsolids, the values of a, a′, b, b′, c and c′ are switched by a first4D-LUT address generating unit controlling memory addresses in the4D-LUTs by according to a result of a 6-vertex solid judging(determining) process performed by a 6-vertex solid judging(determining) unit. However, since d and d′ are common parameters forall of the six vertices, addresses of d and d′ in the 4D-LUT aredetermined by a second 4D-LUT address generating unit according only tothe higher-order data of the signals C, M, Y and K without using theresult of the 6-vertex solid judging (determining) process, as shown inFIG. 24.

[Eighth Embodiment of a Color Converting Device]

In the above-described fifth to seventh embodiments, CMYK data isconverted into RGB data. However, the present invention is not limitedthereto. For example, the present invention is also applicable to acolor conversion of multiband data that is being put into use in thefield of telemedicine.

In general, objects existent in the natural world have variouscharacteristics of spectral reflectance. Therefore, there occurs ametamerism in which two objects appearing to be the same color in acertain lighting environment assume different colors in a differentlighting environment. When such metamerism occurs when performingtelemedicine, a doctor cannot recognize physical conditions of apatient, such as the color of the skin, which hampers a proper medicaltreatment. Thus, for the purpose of reproducing the same color indifferent lighting environments at the doctor side and the patient side,multiband data is being put into use in the field of telemedicine.

With this multiband data, a spectral distribution of an object isrepresented through a multitude of filters having differentcharacteristics of spectral transmittance. Therefore, a color of anobject is represented by, normally, a color signal having 10 componentsor more. Such multidimensional data needs ultimately to be convertedinto three-dimensional data so as to be displayed on a monitor screen,which necessitates a color converting means for convertingmultidimensional an input color signal into such a signal as athree-dimensional color signal.

The color converting device according to the present invention is usablealso in converting n-dimensional data into m-dimensional data havingfewer dimensions than the n-dimensional data.

A description will be given of a specific method of converting then-dimensional data into the m-dimensional data. The n-dimensional datacan be converted into (n−1)-dimensional data by performing the linearinterpolations represented by the expressions 1. Successively, repeatingthese linear interpolations reduces the number of dimensions so as totransform an n-dimensional interpolative calculation into anm-dimensional interpolative calculation. FIG. 25 is a flowchart of acolor converting operation according to the present eighth embodiment.Initially in step S201, the number of dimensions (m) is equal to thenumber of dimensions (n). In step S202 (determining means; determiningstep), it is judged (determined) which of vertex solids corresponds toinput image data, as in the step s151 shown in FIG. 21 of the fifthembodiment. When using a tetrahedral interpolation as athree-dimensional interpolative calculation, the number of vertex solidsof the n-dimensional data becomes 4×2^((n−3)). (When using atriangular-prism interpolation, the number of vertex solids of then-dimensional data becomes 6×2^((n−3)).) Then, in step S203 (readingmeans), interpolation parameters corresponding to vertices of theselected vertex solid are read. Next, in step S204 (generating means;generating step), corresponding two vertices are linearly interpolated.This linear interpolation process halves the number of vertices, andreduces the number of dimensions (m) by one. The linear interpolationprocess in the step S204 is repeated until the number of dimensions (m)equals 3 (Yes in step S205). Subsequently, in step S206 (interpolatingmeans; interpolating step), a three-dimensional interpolativecalculation, such as a tetrahedral interpolation or a triangular-prisminterpolation, is performed so as to calculate an output value.

[Description of a Recording Medium]

FIG. 26 exemplifies a hardware configuration of an image processingsystem in which the computer 502 reads a program recorded on a recordingmedium, and executes the program so as to perform the above-describedcolor converting process. As shown in FIG. 26, this image processingsystem is realized by such a device as a workstation or a personalcomputer. The image processing system comprises a CPU controlling theentire system, a ROM storing firmware such as control programs for theCPU, a RAM serving such usage as a work area for the CPU, a hard disk, amouse, a keyboard, a network interface card (NIC), a display fordisplaying image data, and an image forming device such as a colorprinter.

In the above-described configuration, the CPU, the ROM, the RAM and thehard disk together function also as the computer 502 shown in FIG. 14,in which the CPU can have a function as the color converting deviceaccording to the present invention. Besides, the CPU can be providedwith this function in the form of, for example, a software package,specifically in the form of an information recording medium, such as aCD-ROM. Therefore, the image processing system shown in FIG. 26 includesa medium driver (a program reader) driving such an information recordingmedium.

In other words, the color converting device and the color convertingmethod according to the present invention can be realized in aconfiguration in which a program recorded on an information recordingmedium, such as a CD-ROM, is installed into a general purpose computingsystem comprising an image scanner and a display so that amicroprocessor of this image processing device performs the colorconverting process and the color conversion profile creating process. Inthis case, the program used to perform the color converting processaccording to the present invention, i.e., the program used in a hardwaresystem, is provided as being recorded on the information recordingmedium. Not only a CD-ROM but also other mediums, such as a ROM, a RAM,a flexible disk, and a memory card can be used as the informationrecording medium recording the program and other software. The programrecorded on the information recording medium is installed into a storagedevice, such as a hard disk, incorporated in the hardware system, and isexecuted so as to realize the color converting function.

In addition, the program used to realize the color converting device andthe color converting method according to the present invention isprovided not only in the form of a recording medium, but also by meansof communication from a server.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

The present application is based on Japanese priority applications No.2001-031864 filed on Feb. 8, 2001 and No. 2001-252950 filed on Aug. 23,2001, the entire contents of which are hereby incorporated by reference.

1. A color converting device converting input CMYK data into output color data in a predetermined different format, the device comprising: a contrast emphasizing unit emphasizing a contrast of the output color data corresponding to the CMYK data representing a black-character color more than a contrast of the output color data corresponding to the CMYK data representing a non-black-character color.
 2. A color converting device converting input CMYK data into output color data in a predetermined different format, the device comprising: a color conversion profile representing a correspondence of the CMYK data with the output color data; and a color converting unit converting the CMYK data into the output color data by referring to said color conversion profile, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing a black-character color more than a contrast of the output color data corresponding to the CMYK data representing a non-black-character color.
 3. A color converting device converting input CMYK data into output color data in a predetermined different format, the device comprising: a CMYK/colorimetric-value conversion unit converting the CMYK data into a colorimetric value to be measured with respect to an image formed from the CMYK data by an image forming device; a black-character color judging unit judging whether or not the CMYK data represents a black-character color; a calorimetric value correction unit correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said CMYK/colorimetric-value conversion unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said CMYK/colorimetric-value conversion unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a colorimetric-value/output-color-data conversion unit converting said calorimetric value corrected by said colorimetric value correction unit into the output color data, wherein a contrast of the output color data corresponding to the CMYK data judged to represent the black-character color is emphasized more than a contrast of the output color data corresponding to the CMYK data judged to represent the non-black-character color.
 4. The color converting device as claimed in claim 3, wherein said colorimetric value correction unit performs the contrast correction by linearly transforming a dynamic range of a luminous component of the colorimetric value determined appropriate for each of the black-character color and the non-black-character color into a predetermined dynamic range.
 5. The color converting device as claimed in claim 3, wherein said colorimetric value correction unit performs the contrast correction appropriate for the black-character color to said calorimetric value converted from said CMYK data judged to represent the black-character color by linearly transforming a dynamic range of a luminous component of said colorimetric value determined appropriately for the black-character color into a predetermined dynamic range, and performs the contrast correction appropriate for the non-black-character color to said calorimetric value converted from said CMYK data judged to represent the non-black-character color by linearly transforming a dynamic range of a luminous component of said calorimetric value determined appropriately for the non-black-character color into a predetermined dynamic range.
 6. The color converting device as claimed in claim 3, wherein said calorimetric value correction unit corrects said calorimetric value converted from said CMYK data judged to represent the black-character color so that a chroma of said colorimetric value becomes zero.
 7. The color converting device as claimed in claim 3, further comprising a non-black-character color judging unit judges from the CMYK data in a vicinity of a pixel of interest whether or not there exists a pixel of the non-black-character color having a luminosity lower than a predetermined luminosity in the vicinity of said pixel of interest, wherein said colorimetric value correction unit performs said contrast correction appropriate for the non-black-character color with respect to said pixel of interest when said non-black-character color judging unit judges that there exists the pixel of the non-black-character color having the luminosity lower than the predetermined luminosity in the vicinity of said pixel of interest.
 8. A color conversion profile creating device creating a color conversion profile used for converting CMYK data into output color data in a predetermined different format, the device comprising: a CMYK data generation unit generating the CMYK data; a calorimetric value converting unit converting said CMYK data generated by said CMYK data generation unit into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; a black-character color judging unit judging whether or not said CMYK data generated by said CMYK data generation unit represents a black-character color; a colorimetric value correcting unit correcting said calorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said calorimetric value converting unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said colorimetric value converting unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a color conversion profile setting unit setting said color conversion profile by using said calorimetric value corrected by said colorimetric value correcting unit, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color.
 9. The color conversion profile creating device as claimed in claim 8, wherein said colorimetric value correcting unit performs the contrast correction by linearly transforming a dynamic range of a luminous component of the calorimetric value determined appropriate for each of the black-character color and the non-black-character color into a predetermined dynamic range.
 10. The color conversion profile creating device as claimed in claim 8, wherein said calorimetric value correcting unit performs the contrast correction appropriate for the black-character color to said colorimetric value converted from said CMYK data judged to represent the black-character color by linearly transforming a dynamic range of a luminous component of said colorimetric value determined appropriately for the black-character color into a predetermined dynamic range, and performs the contrast correction appropriate for the non-black-character color to said colorimetric value converted from said CMYK data judged to represent the non-black-character color by linearly transforming a dynamic range of a luminous component of said colorimetric value determined appropriately for the non-black-character color into a predetermined dynamic range.
 11. The color conversion profile creating device as claimed in claim 8, wherein said colorimetric value correcting unit corrects said calorimetric value converted from said CMYK data judged to represent the black-character color so that a chroma of said calorimetric value becomes zero.
 12. The color conversion profile creating device as claimed in claim 8, wherein said CMYK data generation unit generates the CMYK data corresponding to a plurality of representative points in a four-dimensional color space defined by four components of CMYK, and said color conversion profile setting unit creates a four-dimensional lookup table as said color conversion profile, the four-dimensional lookup table representing correspondences of said representative points with respective values of the output color data.
 13. A color conversion profile creating method creating a color conversion profile used for converting CMYK data into output color data in a predetermined different format, the method comprising: the CMYK data generating step of generating the CMYK data; the colorimetric value converting step of converting said CMYK data generated by said CMYK data generating step into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; the black-character color judging step of judging whether or not said CMYK data generated by said CMYK data generating step represents a black-character color; the calorimetric value correcting step of correcting said calorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said calorimetric value converting step from the CMYK data judged to represent the black-character color by said black-character color judging step, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said colorimetric value converting step from the CMYK data judged to represent the non-black-character color by said black-character color judging step; and the color conversion profile setting step of setting said color conversion profile by using said calorimetric value corrected by said colorimetric value correcting step, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color.
 14. The color converting device as claimed in claim 2, wherein said color conversion profile is created by a color conversion profile creating device including: a CMYK data generation unit generating the CMYK data; a calorimetric value converting unit converting said CMYK data generated by said CMYK data generation unit into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; a black-character color judging unit judging whether or not said CMYK data generated by said CMYK data generation unit represents a black-character color; a colorimetric value correcting unit correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said colorimetric value converting unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said colorimetric value converting unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a color conversion profile setting unit setting said color conversion profile by using said calorimetric value corrected by said calorimetric value correcting unit, wherein said color conversion profile is caused to have said characteristic.
 15. The color converting device as claimed in claim 2, wherein said color conversion profile is created by a color conversion profile creating method including: the CMYK data generating step of generating the CMYK data; the colorimetric value converting step of converting said CMYK data generated by said CMYK data generating step into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; the black-character color judging step of judging whether or not said CMYK data generated by said CMYK data generating step represents a black-character color; the calorimetric value correcting step of correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said calorimetric value converting step from the CMYK data judged to represent the black-character color by said black-character color judging step, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said calorimetric value converting step from the CMYK data judged to represent the non-black-character color by said black-character color judging step; and the color conversion profile setting step of setting said color conversion profile by using said calorimetric value corrected by said colorimetric value correcting step, wherein said color conversion profile is caused to have said characteristic.
 16. An image forming device forming an image by using CMYK data, the image forming device comprising: a color converting device converting the CMYK data generated in the image forming device into output color data in a predetermined different format, the color converting device including: a color conversion profile representing a correspondence of the CMYK data with the output color data; and a color converting unit converting the CMYK data into the output color data by referring to said color conversion profile, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing a black-character color more than a contrast of the output color data corresponding to the CMYK data representing a non-black-character color.
 17. An image forming device forming an image by using CMYK data, the image forming device comprising: a color converting device converting the CMYK data generated in the image forming device into output color data in a predetermined different format, the color converting device including: a CMYK/colorimetric-value conversion unit converting the CMYK data into a colorimetric value to be measured with respect to an image formed from the CMYK data by an image forming device; a black-character color judging unit judging whether or not the CMYK data represents a black-character color; a colorimetric value correction unit correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said CMYK/colorimetric-value conversion unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said CMYK/colorimetric-value conversion unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a colorimetric-value/output-color-data conversion unit converting said colorimetric value corrected by said colorimetric value correction unit into the output color data, wherein a contrast of the output color data corresponding to the CMYK data judged to represent the black-character color is emphasized more than a contrast of the output color data corresponding to the CMYK data judged to represent the non-black-character color.
 18. The image forming device as claimed in claim 16, wherein said color conversion profile is created by a color conversion profile creating device including: a CMYK data generation unit generating the CMYK data; a colorimetric value converting unit converting said CMYK data generated by said CMYK data generation unit into a calorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; a black-character color judging unit judging whether or not said CMYK data generated by said CMYK data generation unit represents a black-character color; a calorimetric value correcting unit correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said calorimetric value converting unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said calorimetric value converting unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a color conversion profile setting unit setting said color conversion profile by using said colorimetric value corrected by said calorimetric value correcting unit, wherein said color conversion profile is caused to have said characteristic.
 19. The image forming device as claimed in claim 16, wherein said color conversion profile is created by a color conversion profile creating method including: the CMYK data generating step of generating the CMYK data; the calorimetric value converting step of converting said CMYK data generated by said CMYK data generating step into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; the black-character color judging step of judging whether or not said CMYK data generated by said CMYK data generating step represents a black-character color; the calorimetric value correcting step of correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said calorimetric value converting step from the CMYK data judged to represent the black-character color by said black-character color judging step, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said colorimetric value converting step from the CMYK data judged to represent the non-black-character color by said black-character color judging step; and the color conversion profile setting step of setting said color conversion profile by using said colorimetric value corrected by said colorimetric value correcting step, wherein said color conversion profile is caused to have said characteristic.
 20. An image forming device forming an image by using CMYK data, the image forming device comprising: a color conversion profile creating device creating a color conversion profile used for converting the CMYK data generated in the image forming device into output color data in a predetermined different format, the color conversion profile creating device including: a CMYK data generation unit generating the CMYK data; a calorimetric value converting unit converting said CMYK data generated by said CMYK data generation unit into a calorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; a black-character color judging unit judging whether or not said CMYK data generated by said CMYK data generation unit represents a black-character color; a colorimetric value correcting unit correcting said calorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said colorimetric value converting unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said colorimetric value converting unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a color conversion profile setting unit setting said color conversion profile by using said calorimetric value corrected by said colorimetric value correcting unit, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color.
 21. The color converting device as claimed in claim 14, further comprising said color conversion profile creating device.
 22. A color converting method for converting input CMYK data into output color data in a predetermined different format, the method comprising: the CMYK/colorimetric-value converting step of converting the CMYK data into a calorimetric value to be measured with respect to an image formed from the CMYK data by an image forming device; the black-character color judging step of judging whether or not the CMYK data represents a black-character color; the calorimetric value correcting step of correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said CMYK/colorimetric-value converting step from the CMYK data judged to represent the black-character color by said black-character color judging step, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said CMYK/colorimetric-value converting step from the CMYK data judged to represent the non-black-character color by said black-character color judging step; and the colorimetric-value/output-color-data converting step of converting said colorimetric value corrected by said calorimetric value correcting step into the output color data, wherein a contrast of the output color data corresponding to the CMYK data judged to represent the black-character color is emphasized more than a contrast of the output color data corresponding to the CMYK data judged to represent the non-black-character color.
 23. A color converting method for converting CMYK data into output color data in a predetermined different format, the method comprising the step of: referring to a color conversion profile so as to convert the CMYK data into the output color data, the color conversion profile being created by a color conversion profile creating device including: a CMYK data generation unit generating the CMYK data; a calorimetric value converting unit converting said CMYK data generated by said CMYK data generation unit into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; a black-character color judging unit judging whether or not said CMYK data generated by said CMYK data generation unit represents a black-character color; a calorimetric value correcting unit correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said colorimetric value converting unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said calorimetric value converting unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a color conversion profile setting unit setting said color conversion profile by using said colorimetric value corrected by said calorimetric value correcting unit, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color.
 24. A color converting method for converting CMYK data into output color data in a predetermined different format, the color converting method comprising the step of: referring to a color conversion profile so as to convert the CMYK data into the output color data, the color conversion profile being created by a color conversion profile creating method including: the CMYK data generating step of generating the CMYK data; the colorimetric value converting step of converting said CMYK data generated by said CMYK data generating step into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; the black-character color judging step of judging whether or not said CMYK data generated by said CMYK data generating step represents a black-character color; the colorimetric value correcting step of correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said colorimetric value converting step from the CMYK data judged to represent the black-character color by said black-character color judging step, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said calorimetric value converting step from the CMYK data judged to represent the non-black-character color by said black-character color judging step; and the color conversion profile setting step of setting said color conversion profile by using said calorimetric value corrected by said colorimetric value correcting step, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color.
 25. A computer readable recording medium storing program code for causing a computer to create a color conversion profile used for converting CMYK data into output color data in a predetermined different format, the recording medium comprising: CMYK data generating program code means for generating the CMYK data; colorimetric value converting program code means for converting said CMYK data generated by said CMYK data generating program code means into a calorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; black-character color judging program code means for judging whether or not said CMYK data generated by said CMYK data generating program code means represents a black-character color; calorimetric value correcting program code means for correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the colorimetric value converted by said colorimetric value converting program code means from the CMYK data judged to represent the black-character color by said black-character color judging program code means, and by performing a contrast correction appropriate for a non-black-character color to the calorimetric value converted by said colorimetric value converting program code means from the CMYK data judged to represent the non-black-character color by said black-character color judging program code means; and color conversion profile setting program code means for setting said color conversion profile by using said calorimetric value corrected by said calorimetric value correcting program code means, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color.
 26. A computer readable recording medium storing program code for causing a computer to convert input CMYK data into output color data in a predetermined different format, the recording medium comprising: CMYK/colorimetric-value converting program code means for converting the CMYK data into a calorimetric value to be measured with respect to an image formed from the CMYK data by an image forming device; black-character color judging program code means for judging whether or not the CMYK data represents a black-character color; calorimetric value correcting program code means for correcting said calorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said CMYK/colorimetric-value converting program code means from the CMYK data judged to represent the black-character color by said black-character color judging program code means, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said CMYK/colorimetric-value converting program code means from the CMYK data judged to represent the non-black-character color by said black-character color judging program code means; and colorimetric-value/output-color-data converting program code means for converting said colorimetric value corrected by said colorimetric value correcting program code means into the output color data, wherein a contrast of the output color data corresponding to the CMYK data judged to represent the black-character color is emphasized more than a contrast of the output color data corresponding to the CMYK data judged to represent the non-black-character color.
 27. A computer readable recording medium storing program code for causing a computer to convert CMYK data into output color data in a predetermined different format, the recording medium comprising: color conversion profile referring program code means for referring to a color conversion profile so as to convert the CMYK data into the output color data, the color conversion profile being created by a color conversion profile creating device including: a CMYK data generation unit generating the CMYK data; a colorimetric value converting unit converting said CMYK data generated by said CMYK data generation unit into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; a black-character color judging unit judging whether or not said CMYK data generated by said CMYK data generation unit represents a black-character color; a calorimetric value correcting unit correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said calorimetric value converting unit from the CMYK data judged to represent the black-character color by said black-character color judging unit, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said calorimetric value converting unit from the CMYK data judged to represent the non-black-character color by said black-character color judging unit; and a color conversion profile setting unit setting said color conversion profile by using said colorimetric value corrected by said calorimetric value correcting unit, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color.
 28. A computer readable recording medium storing program code for causing a computer to convert CMYK data into output color data in a predetermined different format, the recording medium comprising: color conversion profile referring program code means for referring to a color conversion profile so as to convert the CMYK data into the output color data, the color conversion profile being created by a color conversion profile creating method including: the CMYK data generating step of generating the CMYK data; the calorimetric value converting step of converting said CMYK data generated by said CMYK data generating step into a colorimetric value to be measured with respect to an image formed from said CMYK data by an image forming device; the black-character color judging step of judging whether or not said CMYK data generated by said CMYK data generating step represents a black-character color; the calorimetric value correcting step of correcting said colorimetric value by performing a contrast correction appropriate for a black-character color to the calorimetric value converted by said calorimetric value converting step from the CMYK data judged to represent the black-character color by said black-character color judging step, and by performing a contrast correction appropriate for a non-black-character color to the colorimetric value converted by said calorimetric value converting step from the CMYK data judged to represent the non-black-character color by said black-character color judging step; and the color conversion profile setting step of setting said color conversion profile by using said colorimetric value corrected by said colorimetric value correcting step, wherein said color conversion profile has a characteristic of emphasizing a contrast of the output color data corresponding to the CMYK data representing the black-character color more than a contrast of the output color data corresponding to the CMYK data representing the non-black-character color. 29-44. (canceled) 